Photo Illustration by The Daily Beast

UPDATE: Graham Dwyer, who was convicted of the murder of Eileen O’Hara in March, was sentenced to life in prison on April 20. (A life sentence in Ireland often means serving only 7 years though it’s doubtful the Dublin architect will get out before serving 18 years.) The slaying was considered to be one of the grisliest in Ireland's history.

A victim impact report prepared by the victim’s father, Frank O'Hara, was read at the sentencing.

“This trial has been an incredibly difficult experience,” the statement read in part. “It was distressing to see Elaine’s private life laid bare before the nation, despite the fact that she was the victim. It was heartbreaking for us to listen to the texts Elaine received from a depraved and diseased mind. This is our life sentence. There is no parole.”

DUBLIN—To many, Graham Dwyer must have seemed like the ideal husband and father.

But in a sensational murder trial that has riveted Ireland, prosecutors have told a jury that Dwyer, 42, led a secret double life as a twisted sadist who killed a woman who called him “Sir” after the pair shared BDSM sex sessions involving knives, stabbings, and blood.

Appearing via satellite from the United States as a witness in the case, a Maine woman named Darci Day told the court she met Dwyer on a fetish website and he told her that his fantasy was to stab a woman to death during sex. Prosecutors said they found a file on Dwyer’s computer titled “Killing Darci” that detailed her planned rape and murder, the Irish Mirror reported.

On Thursday, the 35th day of the trial, the defendant sat alone in the dock at Central Criminal Court just off the River Liffey. His father, who has been a constant presence in the courtroom, sat on a bench nearby.

Graham Dwyer is accused of killing Elaine O’Hara, a 36-year-old childcare assistant who went missing on August 2012. Her remains were found near Killakee Mountain south of Dublin in September 2013.

A sweet-faced, Cork-born architect, Dwyer lived in an upscale suburb of Dublin with his pretty blond wife, Gemma, who bears a slight resemblance to Gwyneth Paltrow, and their two young children.

The Dwyers met as architecture students in Dublin about 18 years ago. Court testimony from Gemma Dwyer and police indicated that the couple sailed, cycled, gardened, took camping trips, and drove around in a Porsche 911 and Audi TTS.

Their low-key suburban life ended in October 2013, when Dwyer was arrested on suspicion of O’Hara’s murder.

Jurors were told by the prosecution that he wooed willing women on BDSM sites online and stabbed them during sex, a fetish that Dublin prosecutors say led to the murder.

Prosecutors built their case against Dwyer, who denies killing O’Hara, with videos allegedly unearthed from Dwyer’s computer and more than 2,600 text messages gleaned from four phones allegedly used by O’Hara and Dwyer.

It’s not known exactly when the two met, but prosecutors indicated that O’Hara, who had a lengthy history of depression and had been hospitalized numerous times since she was a teenager, had posted on BDSM sites saying she was looking for a “master.”

A friend who met her around 2007 testified that O’Hara said she was seeing a man who liked to cut her, the Irish Independent reported.

Dwyer allegedly texted O’Hara frequently about his violent fantasies and at one point demanded she find him someone to kill, according to text messages introduced at trial.

“My urge to rape, stab and kill is huge,” Dwyer allegedlytexted O’Hara in 2011, a year before she was murdered, the Irish Times reported. “You have to help me control or satisfy it.”

O’Hara texted back: “Control, sir. Not satisfy.”

In a series of harrowing video clips shown in Courtroom 13 this week during Dwyer’s trial, the pain O’Hara and other, unidentified women seemingly endured was evident, according to news reports.

Most of the courtroom except for the jury and media was cleared out because the videos—deleted from Dwyer’s computer and then recovered by police, according to media accounts—were so difficult to watch. Irish newspapers carried red-bannered warnings above headlines about the case, warning readers of the graphic content.

Three of the videos shown in court were of O’Hara, according to media accounts. In them, she could be seen naked, tied up, and gagged while being mounted by a man who appeared to beDwyer who, newspaper reports said, appeared to be stabbing her with a knife in the abdomen and breast as music played in the background. Because of the gag, her screams were muffled but the pain she was experiencing was audible and blood was visible.

“It was deeply upsetting to hear,” columnist Nicola Anderson wrote in the Irish Independent.

On Thursday, lead prosecutor Sean Guerin said another video file taken from Dwyer’s computer showed Dwyer putting a clear plastic bag over O’Hara’s head and tightening a cord around her neck. A police detective who took the stand said police have not identified all the women shown in the other videos, but Gemma Dwyer was not seen in any of them.

It’s not clear if the other women in the videos continued to see Dwyer after the painful sex sessions but O’Hara did, according to the prosecution. The two broke it off at some point, but when Dwyer tried to rekindle the relationship in 2011, she was receptive.

According to the text messages that unspool every day in court, O’Hara called Dwyer “Sir” and he called her his “slave.”

In addition to sexual violence, prosecutors said Dwyer allegedly exerted a sick control over O’Hara by criticizing her weight, her smoking, and her teeth, and by requiring her to groom herself to his specifications and get a tattoo with the word “slave” in her genital area, the Independent reported.

At the same time the prosecution alleges that Dwyer was texting O’Hara about his urges to rape, stab, and even be her “secret killer,” he and O’Hara allegedly exchanged pleasantries about Dwyer’s pregnant wife. O’Hara asked Dwyer if his wife was “in labor yet.” When the child was born in March 2011, he told O’Hara she was a “beautiful baby girl.”

At one point, Dwyer allegedly sent O’Hara texts about three ideas he had for what the two often called “play” or “blood play,” the Irish Times reported. Prosecutors said he used what he thought were untraceable phones for some of the texting.

“I’m having lots of thoughts about killing you,” read one message from a disposable phone to O’Hara.

“First I handcuff you, hang you in bedroom, remove cuffs and it looks like suicide. Second one, we go to woods, I take off your clothes, stab you, bury you, leave your clothes near sea at night, looks like you drowned.”

“OK, sounds feasible,” O’Hara replied.

Another message, which prosecutors said was from Dwyer, read: “Third one is like the first, only I slit your wrists in bath before cuffs.”

O’Hara replied: “Okay sir, but problem, I don’t want to die.” The next text back to her read: “We all have to die sometime, these are ways I can do it without your consent...With your consent I would prefer second one, but you would write suicide note and I would make sure you are unconscious.”

In 50 minutes of testimony on February 25, Gemma Dwyer told of her happy life with her husband, their then 3-year-old son and baby daughter. She walked the long way around the courtroom to avoid her husband and never looked at him while on the stand.

She didn’t flinch when asked by the defense attorney about her identification of the family’s garden shovel, which had been found near O’Hara’s remains.

She said she well remembered that the spade had been missing during the summer of 2013 because she often needed it to clean up litter in their garden from the dog next door.

“I mentioned it to Graham a number of times,” she said. “In the end I just used a plastic spade from the sandpit.”

Lead prosecutor Sean Guerin told the court that if it weren’t for a series of what he told the jury were “remarkable coincidences” in September 2013, Dwyer might never have been caught.

First, he said, fisherman in a remote area noticed something shiny floating in a reservoir where the water was unusually shallow for that time of year, the Irish Times reported. The object turned out to be a bag containing knives, bondage masks, leg restraints, sex toys, a phone, and handcuffs.

Later, a dog led his walker to O’Hara’s remains, and then a detective returned to the area and found more items in the water, including a white vibrator, what Guerin called an “anal plug,” and most important, a set of house keys that were traced to Elaine O’Hara.

“This was, in fact, the nearly perfect murder, but for the fact that 2013 was such a warm summer,” Guerin said.